1. Field of the Invention
The present invention relates to a fluid communication structure that unwastefully and stably supplies a liquid such as ink and the like from an ink tank acting as a liquid accommodating section and the like to, for example, a recording head acting as a liquid use section (including a device called a pen) and the like as well as discharges gas existing in the liquid use section into the liquid accommodating section, and relates to a liquid or ink supply system using the fluid communication structure and to an inkjet recording head and an inkjet recording apparatus using the ink supply system.
2. Description of the Related Art
Recently, liquid-using apparatuses, for example, inkjet recording apparatuses, which form an image on a recording medium by applying ink as a liquid onto the recording medium using, for example, an inkjet recording head, are used in a lot of prints including color prints because they can form small dots at a high density with relatively low noise in recording. As a mode of the inkjet recording apparatuses described above, there is an inkjet recording apparatus which includes an inkjet recording head, a carriage, and a transportation means. The ink jet recording apparatus executes recording by ejecting ink in a main scan process of the recording head. In the inkjet recording apparatus, the inkjet recording head receives the ink supplied from an ink tank unseparably or separably attached to the recording head. The carriage has the recording head mounted thereon and causes the recording head to scan the recording medium in a predetermined direction. The transportation means transports (subscans) the recording medium in a direction perpendicular to the predetermined direction with respect to the recording head. Further, there is an inkjet recording apparatus that has a recording head mounted on a carriage in which the recording head is capable of ejecting color inks of yellow, cyan, magenta, and the like. With this arrangement, the inkjet recording apparatus can print not only a monochrome text image but also a full color test image by changing an ejection ratio of the respective inks.
In the inkjet recording apparatuses described above, a problem arises in the proper discharge of gas, such as air and the like, which is trapped or has been trapped in an ink supply path.
The gas, which enters the interior of the supply system, can be roughly classified into four types of gas according to its origins:                1) gas entering from ink injection ports of a print head or generated in an ink ejecting operation;        2) gas separated from the gas dissolved in the ink;        3) gas entering from the outside through a raw material constituting the ink supply path by gas transmission; and        4) gas entering when a cartridge type ink tank is replaced.        
Incidentally, a very fine liquid path is formed in the inkjet recording head. Accordingly, the ink, which is supplied from the ink tank, is required to be in a very clean state without foreign substances, such as dusts and the like, trapped therein. That is, when foreign substances such as dusts are trapped in the ink, a problem arises in that ejection ports, which are particularly narrow in the ink flow path of the recording head, or a liquid path, which directly communicates with the ejection ports, become clogged with the foreign substances. Accordingly, it may become impossible to normally execute an ink ejecting operation or to recover the function of the recording head.
To cope with the above problem, a filter can be disposed in an ink flow path between the recording head and an ink supply needle pierced into the ink tank to prevent foreign substances from entering a recording head side.
Recently, to realize high speed recording, the number of ejection ports for ejecting ink has increased and a drive signal applied to a device for generating energy for ejecting ink employs an increasingly higher frequency. As a result, an amount of consumption of ink per unit time has increased.
Since an amount of ink passing through the filter is thereby increased, it is effective to dispose a filter having a large area. As such, the ink supply path is enlarged and a pressure loss is caused by the filter. Accordingly, when bubbles are trapped in the ink supply path, they can build up in a space upstream of the filter in the enlarged portion and cannot be discharged, which inhibits the smooth supply of ink. Further, the gas built up in the supply path can become fine bubbles which can be trapped in the ink introduced into the ejection ports and cause faulty ink ejection and the like.
Accordingly, it is desireable to immediately eliminate air built up in the ink supply path. Several methods to meet the desire can be exemplified.
One method is to execute a cleaning operation as described below.
An inkjet recording head executes printing by ejecting liquid ink from ejection ports disposed in confrontation with a recording medium in the form of, for example, droplets. Accordingly, faulty printing may occur due to an increase in viscosity and solidification of ink because an ink solvent evaporated from the ejection ports, due to deposition of dust on the ejection ports, or due to the clogging of the ejection ports caused by the bubbles trapped in the liquid path within the ejection ports.
To overcome this problem, the inkjet recording apparatus is provided with a cap member and a wiping member. The cap member covers the ejection ports of the recording head when no printing operation is executed. The wiping member cleans the surface of the recording head through which the ejection ports are formed (ejection port forming surface) when necessary. The cap member not only functions as a lid for preventing the ink in the ejection ports from being dried when no printing operation is executed, but also functions to refresh the ejection ports clogged with solidified ink and for overcoming faulty ink ejection caused by an increase in viscosity of the ink in a liquid path and trapped bubbles. This function is executed when the ejection ports are clogged by covering the ejection port forming surface with the cap member and sucking and discharging ink from the ejection ports by applying a negative pressure thereto from a suction pump that communicates with the inside of the cap member.
The forcible ink discharge process for overcoming the faulty ink ejection is a called a cleaning operation. This is executed when printing is resumed after the recording apparatus is out of operation for a long period of time and when a user turns on, for example, a cleaning switch by recognizing that quality of a recorded image is deteriorated, and the like. Further, after ink is forcibly discharged by the cleaning operation, a wiping operation is executed on the ejection port forming surface with the wiping member composed of an elastic plate such as a rubber plate.
In a cleaning operation executed when a flow path and a liquid path of the recording head are initially filled with ink and when an ink tank is replaced, there is executed a trial for discharging built-up bubbles by applying a large negative pressure to the capped ejection port forming surface by driving the suction pump at high speed and obtaining a high flow speed of ink in an ink supply path.
However, an increase in the area of the filter for suppressing a dynamic pressure of the filter increases a sectional area of the flow path. Accordingly, even if the large negative pressure is generated in the flow path by the cleaning operation described above, a high flow speed, at which bubbles can be effectively transferred, cannot be generated, and thus it is very difficult to eliminate remaining bubbles from the ejection ports by the suction pump. That is, the ink passing through the filter must be provided with a predetermined flow speed as a condition in which bubbles are caused to pass through the filter by the ink flow generated by the suction pump. For this purpose, however, a large pressure difference must be generated on both sides of the filter to obtain the predetermined flow speed. To realize the large pressure difference, it is ordinarily contemplated to increase a flow path resistance by reducing the area of the filter or to increase a flow amount of the suction pump. However, when the filter is reduced in size, an ink supply performance to the recording head is deteriorated. Further, when it is intended to eliminate gas by a large amount of flow of ink, a large amount of ink is discharged, thereby ink is wastefully consumed.
Therefore, other methods for eliminating bubbles include: (1) a method of directly discharging bubbles to the outside; and (2) a method of moving bubbles to an ink tank side and reserving them in a portion of the ink tank where they do not inhibit an ink supply. In the former method, a communication port to the outside is disposed in an ink supply path, which is not preferable because of the reasons described below.
That is, some inkjet recording apparatuses have a capillary force generation member such as an absorbent and the like disposed in an ink tank to prevent the unpreferable leakage of ink from ejection ports. Alternatively, they generate a negative pressure in an ink accommodation space of the ink tank by applying an urging force in a direction where the volume of a flexible ink accommodation bag is increased, the urging force being generated by an elastic member such as a spring or the like disposed to the bag. In this case, when a simple communication port is disposed to the ink supply path to eliminate bubbles, the negative pressure is released by the air entering from the communication port. To cope with the problem, a pressure regulation valve or the like must be disposed to the communication port. However, an ink supply system and a recording apparatus using the system are made complex in structure and increased in size. Further, a water repellent membrane or the like, through which gas can pass but a liquid cannot pass, must be provided to prevent the leakage of ink from the communication port for discharging bubble, or a device (composed of a bubble quantity sensor, a communication path opening/closing mechanism, and the like) is necessary to open the communication port and to discharge bubbles only when they build up. However, manufacturing costs are increased, and the structure of the recording apparatus is made complex and the size thereof is increased.
In contrast, it is examined to move bubbles to the ink tank side. At the time, if an amount of ink, which corresponds to the volume of the bubbles moving to the ink tank, can be transferred to the recording head side, a volume inside the ink tank does not change. This is preferable because a generated negative pressure can be kept constant, and a negative pressure, which balances a holding force of a meniscus formed to ejection ports, can be applied to the recording head. Further, when a cartridge type ink tank is employed, the ink tank can be replaced with a new ink tank when an amount of the ink remaining therein decreases. Thus, it can be said that the above arrangement can completely eliminate gas from an ink supply system.
Many consumer inkjet recording apparatuses are arranged such that a cartridge type ink tank, in which black and color inks are accommodated, respectively, is detachably mounted above a recording head or on a carriage, on which the recording head is mounted. That is, many of ink cartridges begin to supply ink into a recording head when, for example, a hollow ink supply needle, which is mounted on a carriage upward, is pierced thereinto. Accordingly, attention must be paid to an inside diameter of the ink supply needle that couples the ink cartridge with the recording head. This is because although a thin supply needle is preferably used to execute a cartridge mounting operation simply without the need for a large force, a decrease in the inside diameter of the needle increases a meniscus force, by which smooth movement of bubbles is made difficult.
Incidentally, several proposals have been made as to a mechanism for moving gas to an ink tank side.
For example, Japanese Patent Laid-Open No. 5-96744 (hereinafter, referred to as “patent document 1”) discloses that a recording head side is divided into a first chamber having an atmosphere communication port and a second chamber having a capillary force generation member. The first chamber is coupled with an ink tank through at least two communication paths disposed on the first chamber side. These communication paths include openings having different heights. With this arrangement, air is supplied to the ink tank side through one of the communication paths to the ink tank side. In the above arrangement, a negative pressure is applied to a recording head by a difference of water heads between the first and second chambers or by the capillary force generation member disposed in the second chamber, and thus the atmosphere communication path can be disposed to the first chamber.
However, an object of the arrangement of the patent document 1 is to introduce outside air into the ink tank as ink is supplied therefrom in order to completely use the ink in the ink tank which does not deform. Accordingly, it is not an object of the patent document 1 to discharge bubbles remaining in an ink supply path into the ink tank. That is, the technology disclosed in the patent document 1 cannot be applied to transfer even gas from the ink supply path, in particular, from the second chamber or the recording head side into the ink tank.
Further, as another proposal, Japanese Patent Laid-Open No. 11-309876 (corresponding U.S. Pat. No. 6,460,984) (hereinafter, referred to as “patent document 2”) discloses that when a negative pressure generation member accommodating chamber is separable from a liquid accommodation chamber, a gas-introduction-oriented path and a liquid taking-out path are disposed to a communicating section that couples the negative pressure generation member accommodating chamber with the liquid accommodation chamber in order to securely introduce gas into the liquid accommodation chamber. However, the patent document 2 also discloses a capillary force generation member and an atmosphere communication port disposed between an ink tank and a recording head. Accordingly, the patent document 2 discloses an ink supply path opened to the atmosphere in which gas is free to enter into and exit from the ink supply path through an opening acting as the atmosphere communication port similar to the patent document 1. Accordingly, the technology disclosed in the patent document 2 cannot be applied for eliminating the bubbles remaining in the ink supply path.
Further, U.S. Pat. No. 6,347,863 (hereinafter, referred to as “patent document 3”) discloses an ink container (50) having a drain conduit (66, 72, 74) and a vent conduit (76, 82, 84) each projecting downward from the ink container (50). In this arrangement, the drain conduit has an upper opening formed to the bottom of an inner wall of the ink container, and the vent conduit has an opening disposed inside of the accommodation space of the ink container. An object of the technology disclosed in the patent document 3 is to arrange a system for refilling ink to a member (14) having a reservoir (16, 18, 20). It is not an object of the patent document 3 to eliminate bubbles remaining in an ink supply path located downstream of the reservoir and in portions in which ink is used. Further, since a lower opening of the drain conduit and a lower opening of the vent conduit have the same height, it is contemplated that when a meniscus is formed in the conduits, a liquid and gas cannot move therein. Further, although the patent document 3 does not disclose an atmosphere communication port, it is contemplated that it is disposed anywhere. This is because if a system composed of the ink container (5) and the member (14) is hermetically sealed, the internal negative pressure of the system increases abruptly as ink is continuously used, and the ink cannot be supplied to the portion in which the ink is used. Accordingly, it is assumed that the atmosphere communication port is disposed to the reservoir (16, 18, 20) in consideration of a foam (90) accommodated in the reservoir (16, 18, 20) and the arrangement and function of the ink container, the drain conduit, and the like. However, the patent document 3 does not have a standpoint for positively eliminating the bubbles remaining in the ink supply path because of the reasons described in the above items 1) to 4) in any case.
Japanese Patent Laid-Open No. 10-29318 (corresponding U.S. Pat. Nos. 5,963,237, 6,022,102 and 6,276,784) (hereinafter, referred as “patent document 4”) discloses that an ink replenishment tank can be coupled with a reservoir tank. The reservoir tank includes a negative pressure generation member accommodating chamber and an ink accommodation chamber. The ink replenishment tank replenishes ink to the reservoir tank. In the above arrangement, when the replenishment tank is coupled with a space in the ink accommodation chamber at upper and lower portions of the ink accommodation chamber, ink is introduced from the replenishment tank into the ink accommodation chamber through a lower liquid communication pipe, and air is introduced from the ink accommodation chamber into the replenishment tank through an upper gas communication pipe. However, the arrangement of the patent document 4 is similar to the arrangements of the patent documents 1 and 2 in that a negative pressure generation member and an atmosphere communication port are interposed between the ink accommodation chamber and a recording head. Accordingly, the technology disclosed in the patent document 4 cannot be applied to an object of eliminating bubbles remaining in the ink supply path.
Further, Japanese Patent Laid-Open No. 2001-187459 (corresponding U.S. Pat. No. 6,520,630) (hereinafter, referred to as “patent document 5”) discloses that a subtank 1022 is mounted above a main tank 1020 to replenish ink into the main tank 1020 that communicates with a recording head 1018 as shown in FIG. 16. The gas in the main tank is introduced into the subtank and the ink in the subtank is supplied into the main tank as a carriage is accelerated and decelerated. In the patent document 5, the main tank communicating with the subtank accommodates ink in a free state. However, since the main tank includes means for introducing outside air thereinto, the arrangement of the patent document 5 is not essentially different from those of the patent documents 1, 2, and 4. That is, the patent document 5 does not have a standpoint for positively eliminating the bubbles remaining in an ink supply path because of the reasons shown in the items 1) to 4).
An arrangement common to the patent documents 1, 2, 4, and 5 resides in that the separable liquid accommodation unit (ink tank) communicates with the recording head through a plurality of the communication paths and that the atmosphere introduction means is provided downstream of the communication paths (on the recording head side). A problem arising in the above arrangement will be explained with reference to the patent document 5.
FIG. 16 is a conceptual view explaining the invention disclosed in the patent document 5. In a state shown in FIG. 16, a balance of forces acting on a meniscus formed by a pipe 1056A will be examined assuming that movement of air stops (movement of gas to a subink chamber 1081 of the subtank 1022 through the pipe 1056A). First, a downward-acting force includes a pressure HA and a meniscus force, the pressure HA being generated by a difference of water heads between the liquid surface of the ink in the subink chamber 1081 and the position of a meniscus formed in an opening the pipe 1056A. Further, an upward-acting force includes a pressure P generated by the air reserved in an ink bag 1100 disposed in the main tank 1020. The movement of air is stopped because all the forces are balanced. In this case, the air pressure P balances a sum of the pressure, which is generated by a difference of water heads between the liquid surface of the ink in the subink chamber 1081 and the liquid surface position of the ink in the ink bag 1100, and the pressure generated by the meniscus (P=HA+MA). Further, since the ink in the subink chamber 1081 communicates with the ink in the ink bag 1100 through a pipe 1056B, a difference between a downward acting ink pressure that acts on the meniscus formed in the pipe 1056A and the gas pressure in the ink bag 1100 is equal to a pressure HB−HA generated by a difference of water heads between the meniscus position in the pipe 1056A and the liquid surface in the ink bag 1100. As a result, the balanced state is achieved by that a pressure HB−HA generated by the difference of the water heads balances the meniscus pressure MA.
When the liquid level in the ink bag 1100 falls because ink is further consumed from the above state and bubbles are introduced from a bubble generator 1104, and the like, the pressure HB−HA, which is generated by the difference of the water heads between the meniscus position in the pipe 1056A and the liquid level in the ink bag 1100, increases. Then, when the pressure HB−HA finally exceeds the meniscus pressure, air is introduced into the subink chamber 1081, thereby the ink in the subink chamber 1081 is supplied into the ink bag 1100.
However, when ink is ejected by the recording head 1018, since an ink flow is generated in an overall supply system, a pressure loss is generated between the subink chamber 1081 and the ink bag 1100 based on an amount of ink flowing in the pipe 1056B. Accordingly, the pressure loss must be further taken into consideration, in addition to the relation between the meniscus pressure MA described above and the pressure HB−HA generated by the difference of the water heads between the meniscus position and the liquid surface in the ink bag 1100. As a result, air moves when the pressure generated by the above difference of the water heads exceeds the meniscus pressure to which the pressure loss is added. That is, a gas/liquid exchange does not occur unless the liquid surface falls by the pressure loss in the pipe 1056B according to the amount of flow of the ink in an ink ejection state, i.e. in a dynamic state as compared with the air movement stop state. When the liquid surface in which the gas/liquid exchange is to be started becomes lower than the opening of the pipe 1056B, the gas/liquid exchange does not occur, and the ink in the main tank 1020 is completely consumed without using the ink in the subtank 1022.
Accordingly, when the pipe is made thin to simply and easily mount the ink tank as described above, the pressure loss is increased thereby, and thus it must be taken into consideration that the position of the liquid surface, at which the gas/liquid exchange starts in the main tank, falls in correspondence to the increase of the pressure loss. That is, the main tank cannot help being increased in size, by which the recording apparatus is increased in size in its entirety.
Further, it is another problem of the arrangement shown in FIG. 16 that the bubble generator 1104 is disposed under the main tank. That is, there is a possibility that bubbles introduced from the bubble generator 1104 are carried by the flow of ink traveling to the recording head 1018 and pulled into a flow path 1041 that communicates with the recording head 1018 as an ink ejecting operation is executed regardless that it is very preferable to minimize the bubbles that are transferred to ink ejection ports. To prevent the bubbles from being pulled into the flow path 1041, it is necessary to employ a countermeasure for restricting the flow of the ink resulting from the ink ejecting operation and for disposing the bubble generator 1104 at a position apart from a filter 1039, which further increases the size of the main tank 1020.
These disadvantages also occur in the arrangements of the patent document 1, 2, 4 in which the atmosphere introduction means is disposed at a position nearer to the recording head than the communication path.
As described above, the patent documents 1 to 5 disclose to introduce gas into the ink tank located at an uppermost stream position. However, these documents do not satisfy an object of smoothly transferring the gas, which enters the ink supply path having the hermetically-sealed structure in use because of the reasons described in the above items 1) to 4) and builds up therein, into the ink tank and reserving it therein. Further, when an amount of flowing ink increases to execute printing at high speed, an ink supply may not follow the increasing amount of the flowing ink and may be interrupted or bubbles may be trapped in the recording head. To overcome these drawbacks, the recording head cannot be help being increased in size.